One of the process steps commonly encountered in the fabrication of integrated circuits and other semiconductor devices is photolithography. Broadly, photolithography involves selectively exposing a specially prepared wafer surface to a source of radiation using a patterned template to create an etched surface layer. Typically, the patterned template is a reticle, which is a very flat glass plate that contains the patterns to be reproduced on the wafer. Typical reticle substrate material is optically clear quartz. Because of the tiny size of the critical elements of modern integrated circuits, the operative surface of the reticle (i.e. the patterned surface) is kept free of contaminants that could either damage the surface or distort the image projected onto the photoresist layer during processing, both of which lead to a final product of unacceptable quality.
Generally, reticles are stored and/or transported within a mini-clean room type environment created within a SMIF container or pod having a base and a cover. The cover mates with the base to form a hermetically sealed enclosure for holding the reticle.
Considering the severe impact of particulates on semiconductor fabrication, unnecessary and unintended contact between the reticle and other surfaces during manufacturing, processing, shipping, handling, transport or storage is highly undesirable in view of the susceptibility of the reticle to damage to the delicate features on the patterned surface due to sliding friction and abrasion. Also, any particulate contamination of the surface of the reticle can compromise the reticle to a degree sufficient to seriously affect any end product obtained from the use of such a reticle during processing. Particles can be generated within the controlled environment containing the reticle during processing, transport and shipping. Sliding friction between the reticle and the container and between the components of the container are sources of contaminating particulates. Also, it is now known that gases and minute quantities of moisture can escape from the polymer materials used in reticle containers, such can cause haze and crystal growth on reticles damaging same.
Photolithography is moving towards utilizing extreme ultraviolet (EUV) light sources with shorter wavelengths that permit production of smaller sized integrated circuits, often in a vacuum environment, thus imposing heightened functional requirements on a container or pod designed to store, transport and ship a reticle destined for EUV photolithography use. For example small particles that are not big enough to cause a problem in conventional photolithography can be a significant problem in EUV photolithography. Also, EUV photolithography can be performed under a vacuum which can make outgassing and/or moisture desorption from container components an issue, particularly when the components are polymers.
Pods used for EUV lithography typically utilize an inner pod and an outer pod. Examples can be found at U.S. Pat. No. 8,231,005 to Kolbow et al. (“Kolbow”) and U.S. Pat. No. 7,607,543 to Gregerson et al. (“Gregerson”), both owned by the owner of the instant application and the disclosures of which are hereby incorporated by reference herein in their entirety except for express definitions contained therein. The inner pod is conventionally metal to eliminate outgassing or moisture desorption common with polymers and to provide a machined planar surface to planar surface seal. Aluminum with an electroless nickel plating thereon is suitable. The sealing of the inner pod as disclosed by Kolbow is a flat metallic surface to a flat metallic surface.
A concern is that particulate generation and entrapment that heretofore was tolerated in reticle pod carriers can become problematic in the context of carriers containing reticles for EUV photolithography use (e.g., particles generated between vertically sliding surfaces when the cover is mounted to the base, and particles entrapped between fasteners and fastened surfaces). A system that addresses such particle generation and entrapment would be a welcomed advance in photolithography generally and in EUV photolithography in particular.